Conventionally, there has been proposed a retrieval system that receives a query and can output an answer to the query.
For example, an example of a similar document retrieval system, which uses a query as input, has been disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 11-66086).
The similar document retrieval system includes a question input unit, a keyword dividing unit, a keyword similarity calculating unit, a threshold value setting unit, a highly similar document discriminating unit, a full similarity accumulating and sorting unit, and an answer output unit.
This similar document retrieval system is operated as follows.
The keyword dividing unit divides a keyword from a retrieval question inputted from the question input unit. The keyword similarity calculating unit calculates the similarity between each keyword and each object document to be searched. The highly similar document discriminating unit discriminates documents, which have similarity with a prepared threshold value or more, by using the calculated similarity. The full similarity accumulating and sorting unit accumulates the similarity of each document on the basis of all the discriminated documents. The answer output unit makes an answer of the summed-up similarity of each document.
Further, an example of a similar document retrieval system, which is to obtain information requested by a user with high accuracy, has been disclosed in Patent Document 2 (Japanese Patent Application Laid-Open No. 2004-139553).
The similar document retrieval system includes a query input unit, a retrieval keyword extracting unit, a retrieval keyword type assignment unit, a retrieval question type decision unit, a retrieval keyword classification unit, a keyword classification rule storage unit, a document retrieval unit, and an retrieval object document storage unit.
This similar document retrieval system is operated as follows.
The query input unit receives a query inputted by a user. The retrieval keyword extracting unit analyzes the inputted query to extract retrieval keywords. The retrieval keyword type assignment unit decides the type of each extracted retrieval keyword, and assigns a keyword type. The retrieval question type decision unit decides the question type.
The retrieval keyword classification unit classifies the retrieval keywords, to which the keyword types are assigned, into a major type and a minor type with reference to the question type and the keyword classification rules stored in the keyword classification rule storage unit. The document retrieval unit searches retrieval object documents stored in the object document storage unit by using the classified search keyword groups, and thus obtains the documents of the retrieved result.    Patent Document 1: Japanese Patent Application Laid-Open No. 11-66086    Patent Document 2: Japanese Patent Application Laid-Open No. 2004-139553